Propane Fueled Fast Cook-Off Burner

ABSTRACT

A propane burner assembly is provided for producing a fast cook-off environment. The burner assembly includes a frame, parallel delivery pipes, a pair of manifolds with a corresponding pair of feed lines, a supply line, a fuel reservoir, a valve and an igniter pilot. The frame geometrically defines a platform region with a plurality of corners. The frame includes at least two opposite sides. The delivery pipes are supported by the frame. Each delivery pipe has a plurality of orifices. The manifold pair supplies propane to the delivery pipes. The manifolds are respectively disposed adjacent the two opposite sides. The feed lines transport propane to the manifolds. The fuel reservoir stores the propane. The supply line delivers propane from the fuel reservoir to the feed lines. The valve controls delivery of propane to the feed lines. The igniter pilot initiates combustion. Activating the valve enables propane to eject through the orifices to propagate combustion within the frame.

CROSS REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119, the benefit of priority from provisional application No. 62/194,778, with a filing date of Jul. 20, 2015, is claimed for this non-provisional application.

STATEMENT OF GOVERNMENT INTEREST

The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND

The invention relates generally to producing an environmentally compliant fast cook-off test fixture. In particular, the invention relates to a propane burner with feed tubes for subjecting munitions to convective and radiative based fuel fire in thermal reaction testing.

The Department of the Navy has tested weapons that contain energetic material (e.g., explosives, pyrotechnics, solid propellants, etc.) to combustion environments so as to induce cook-off, such as supplied by a burning kerosene pool. These tests are necessitated in support of programs to reduce thermal vulnerability of munitions. As energetic materials rise in temperature, their chemical bonds decompose or rupture, causing exponential self-initiated thermal generation. This self-heating process can eventually lead to uncontrolled detonation, explosion, deflagration or burning.

SUMMARY

Conventional cook-off burners yield environmental disadvantages addressed by various exemplary embodiments of the present invention. In particular, exemplary embodiments provide a propane burner for producing fast cook-off environments. The exemplary burner includes The burner assembly includes a frame, parallel delivery pipes, a pair of manifolds with a corresponding pair of feed lines, a supply line, a fuel reservoir, a valve and an igniter pilot. The frame geometrically defines a platform region with a plurality of corners. The frame includes at least two opposite sides. The delivery pipes are supported by the frame. Each delivery pipe has a plurality of orifices. The manifold pair supplies propane to the delivery pipes. The manifolds are respectively disposed adjacent the two opposite sides.

In exemplary embodiments, the feed lines transport propane to the manifolds. The fuel reservoir stores the propane. The supply line delivers propane from the fuel reservoir to the feed lines. The valve controls delivery of propane to the feed lines. The igniter pilot initiates combustion. Activating the valve enables propane to eject through the orifices to propagate combustion within the frame. Other various embodiments additionally provide for thermocouples and directional slug calorimeter as instrumentation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which:

FIG. 1 is a perspective view of an exemplary burner configuration;

FIG. 2 is a perspective view of the burner in combustion operation;

FIG. 3 is a plan view of the exemplary burner configuration;

FIG. 4 is a schematic view of fuel control for the exemplary burner;

FIG. 5 is a perspective view of instrumentation arrangement for the exemplary burner;

FIG. 6A is an elevation cross-section view of a directional slug calorimeter (DSC);

FIG. 6B is a perspective view of the DSC;

FIG. 7 is a tabular view of quantitative characteristics for the DSC;

FIG. 8 is a diagram view of a temperature measurement array; and

FIG. 9 is a diagram view of a heat flux quantity array.

DETAILED DESCRIPTION

In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

Exemplary embodiments of a propane fast cook-off burner provide advantages over conventional pool fire burners, including reduced environmental pollution, cleaner and less expensive fuel, and improved safety from ignition control. Additional advantages include reductions in fuel consumption, post-test soot residue, post-test hazardous waste (from unburned jet fuel and combustive reaction residue) over conventional configurations.

FIG. 1 shows a perspective view 100 of an exemplary propane burner assembly 110. A square horizontal frame 120 supports vertical posts 130 and is disposed on a ground base 140. Panel shield walls 150 are disposed between the posts 130 to confine flames along the sides of a burner platform 160 for cook-off testing within the frame 120. A fuel feed-line 170 forks into supply lines 180 that enter manifolds 190. These lines 170, 180 and 190 transport fuel for burning on the platform 160.

FIG. 2 shows a perspective view 200 of the burner assembly 110 in combustion operation exhibiting a fire plume 210. The burner assembly 110 is shown with the panels 150 obscuring the platform 160 from which the plume 210 originates. Due to the fuel-rich conditions, the flames from the exemplary burner 110 originate above the platform 160 to provide soot within the flames (rather than in the plume). The soot facilitates uniform radiation heating of a target munition for fast cook-off testing, rather than bottom heating as typical in conventional stoichiometric combustion.

FIG. 3 shows a plan view 300 of the exemplary burner assembly 110. An insert view 310 shows a perspective view of the assembly 110. A compass rose 320 shows the exemplary direction of north. The fuel feed-line 170 supplies fuel from a source from south of the frame 120 and divides at a T-joint into the supply lines 180 east (up) and west (down) in the view 300. The supply lines 180 feed the manifolds 190 that flank the frame 120. An ignition torch 330 on the frame 120 and controlled via a cable 340 initiates combustion of fuel ejected from parallel delivery pipes 350 supplied through the manifolds 190. In the exemplary configuration, the frame 120 is twelve feet on each side, and separation between delivery pipes 350 is five inches. These exemplary dimensions are illustrative of a tested design, and are not limiting. Other propane burner configurations with alternate dimensions (for a variety of FCO test articles) can be considered for such purposes without departing from the scope of the claims. Alternate hydrocarbon fuels besides propane that are in gaseous phase at standard temperature and pressure can also be contemplated.

The manifolds 190 connect to interleaving pipes 350 by unions 360, with adjacent pipes 350 sealed by caps 370. The insert view 310 includes a corner detail 380, which in its enlarged portion shows a portion of the delivery pipes 350 and the orifices 390 arranged therealong at spacing intervals of five inches. After cook-off of a tested munition, damaged pipes 350 can be disconnected from the manifold 190 at their corresponding unions 360 and replaced.

FIG. 4 shows a schematic view 400 of an exemplary fuel control configuration 410. A fuel tank 420 supplies fuel for the feed-line 170. A burner 430 and pilot 440 provide combustion initiators. A legend 450 identifies instrumentation and control devices. Remote solenoid valves 460 include the tank exit 462, burner entrance 464 and pilot entrance 466. Manual valves 470 include the first valve 472 at the tank exit, second valve 474, third valve 476 before the fork, and fourth valve 478 leading to the pilot 440. Pressure transducers 480 include positions at the tank exit 482, burner entrance 484 and pilot entrance 486. Regulators 490 include the burner entrance 492 and the pilot entrance 494.

FIG. 5 shows perspective views 500 of thermal instrumentation arrays for the exemplary burner assembly 110. An upright frame 510 contains the instrumentation shown as a north-south array 520 and an east-west array 530. The arrays 520 and 530 are about eight feet across and six feet high. The instrumentation arrays were employed for evaluating performance of the burner assembly 110, but are not used for cook-off tests with munitions.

FIGS. 6A and 6B show detail views 600 of a directional slug calorimeter (DSC) assembly 610. FIG. 6B shows an isometric view, including a tubular housing 620 with longitudinal grooves 630, while FIG. 6A shows a cross-section elevation view of that housing 620, which is subdivided into four symmetric quadrants. The assembly further includes a support tube 640, a thermocouple 650, and connectors 660. The housing 620 is divided into four quadrants 670, separated by isolation cut interfaces 680. The thermocouple 650 is disposed in each groove 630 and internal insulation 690. The DSC 610 is described in greater detail in application Ser. No. 14/293,078, published as publication 2015/0346042, being incorporated by reference in its entirety.

FIG. 7 shows a tabular view 700 of parameters for properties of the DSC 610. The Table includes a left column 710 with Parameters and a right column 720 with exemplary values and their associated units. The parameters include surface area, emissivity, Stefan-Boltzmann constant, mass and curve-fit coefficient.

FIG. 8 shows an elevation view 800 of the thermocouple measurements array. The left array 810 shows the temperature values from instrumentation 530 looking to the north. The right array 820 shows the temperature values from instrumentation 520 looking to the west. Temperatures are shown in degrees Celsius (° C.). Both arrays 810 and 820 provide orthogonal planes discretized into grids.

FIG. 9 shows an elevation view 900 of the heat flux values array on a first side 910 and a second side 920 of the burner. Individual values 930 in particular cells show heat flux in kilowatts-per-square-meter derived from calorimetry measurements from view 800. These values range from 40 kW/m² at the extremities to 115 kW/m² along the centerline. The sides are arranged along and adjacent to a centerline 940.

Fast cook-off testing using liquid hydrocarbon fuel pits has been a standard test method for insensitive munition classification. Recently, environmental concerns over the pollution caused by these tests have pushed many nations to examine candidates for a cleaner alternative. This disclosure describes efforts within the Department of the Navy to develop and characterize an exemplary propane fueled burner assembly 110 that produces thermal stimuli similar to that produced by a liquid hydrocarbon pool fire. The burner transports liquid propane from a fuel tank 420 into a number of delivery pipes 350 within the hearth of the test area platform 160.

Once ignited, radiative feedback from the fire plume 210 vaporizes the liquid propane within the tubes to produce propane gas that exits the delivery pipes 350 and combusts within the burner platform 160. The resulting fire (as exhibited by plume 210) is very fuel rich in the test region (bounded by the panels 150) with sufficient soot to produce the thermal radiation levels seen in typical liquid hydrocarbon fueled combustion.

To verify the thermal characteristics of the propane fire in the exemplary burner 110, both temperature and heat flux measurements were collected, with examples respectively shown in views 800 and 900. Testing demonstrates that the propane burner produced temperatures that were comparable to those produced by a liquid hydrocarbon fueled fire and satisfied the temperature requirements of STANAG 4240. Additionally, and perhaps more importantly, total heat flux measurements were also similar between the two fires. Both temperature and heat flux measurements showed that the heating was also uniform within the burner 110. The totality of these results indicates that the exemplary propane burner 110 produced by the Navy Department is an acceptable alternative to liquid hydrocarbon pool fires for fast cook-off testing.

Fast cook-off (FCO) testing is a standard insensitive munitions test that is used to determine how munitions react when subjected to rapid heating. These tests are used to simulate real-world scenarios such as carrier deck fires or transportation accidents where ordinance items have the potential to be exposed to a fire. Traditionally, these tests have been performed by positioning the item over large pools of liquid hydrocarbon fuels such as kerosene or jet fuel. During the test, the fuel is ignited and the item is completely engulfed in the flame. The response of the item to this fire exposure is then measured. This response can range from a severe detonation (type I) to more mild reactions such as burning (type V) or no reaction whatsoever (type VI). The goal of weapon development is to produce ordnance items that have the mildest possible reaction during FCO testing in order to mitigate hazards aboard combat vessels of ordnance on board. These conditions exhibited their deadly effect in the devastating fire and explosions that killed 134 sailors aboard the U.S.S. Forrestal in July 1967.

The fuel-fire test is required by both the Department of Defense Explosive Safety Board (DDESB) and the Insensitive Munitions (IM) office in the United States. The fuel-fire test is specified as the liquid fuel, external fire test as described in TB 700-2 for hazards classification relative to transportation and storage while operational scenarios are covered in MIL-STD-2105D. These tests are performed at a system level in accordance to STANAG 4240, “Liquid Fuel/External Fire, Munition Test Procedures” (2003) issued by NATO.

In recent years however, environmental pressure has forced nations to re-examine how they perform FCO testing. The large black clouds of soot produced by these tests attract unwanted attention from communities surrounding test sites. Additionally, the large open pools of fuel create the opportunity for spills leading to ground contamination. These environmental concerns prompted a debate on whether a cleaner alternative could be used for FCO testing. 

1. A propane burner assembly for producing a fast cook-off testing environment, said burner assembly comprising: a frame that geometrically defines a platform region with a plurality of corners, said frame having first and second sides opposite each other; a parallel plurality of delivery pipes supported by said frame, each delivery pipe having a plurality of orifices; first and second manifolds to supply propane to said delivery pipes, said manifolds being respectively disposed adjacent said first and second sides; first and second feed lines to transport said propane to said manifolds; a fuel reservoir for storing said propane; a supply line for delivering said propane from said fuel reservoir to said feed lines; a valve for controlling delivery of said propane to said feed lines; and an igniter pilot for initiating combustion, wherein activating said valve enables said propane to eject through said orifices to propagate said combustion within said frame;
 2. The burner assembly according to claim 1, wherein said frame further includes a post at each corner of said plurality of corners, with a panel disposed between each pair of posts.
 3. The burner assembly according to claim 1, wherein same valve is a solenoid valve.
 4. The burner assembly according to claim 1, wherein said manifolds supply said propane to alternating delivery pipes.
 5. The burner assembly according to claim 1, further including an instrumentation structure for disposing a plurality of thermal measurement instruments, each instrument being arranged in a grid.
 6. The burner assembly according to claim 5, wherein said instrument is a thermocouple.
 7. The burner assembly according to claim 5, wherein said instrument is a directional slug calorimeter.
 8. The burner assembly according to claim 1, where in said platform region is rectangular.
 9. The burner assembly according to claim 4, wherein said adjacent delivery pipes are antiparallel.
 10. The burner assembly according to claim 1, wherein said fuel reservoir stores a fuel mixture of propane and at least one of methane, ethane and butane. 